Current surgical pathology practice consists of having a pathologist receive a surgical specimen immediately after resection. The pathologist marks the specimen with ink to show how the specimen was oriented in the body (i.e., the blue-inked side was facing forward in the body). The pathologist then slices the specimen into thin (i.e., 3 mm thick) slices, and visually inspects the slices. The pathologist then selects the areas that appear visually to have the greatest likelihood of containing cancer, and removes a small section from these pieces. The pathologist freezes these small pieces and shaves thin sections for rapid staining and inspection under a microscope ("frozen section"). The pathologist conveys his or her impression as to the frozen section results to the surgeon, so that the surgeon can decide whether the resection has been adequate. If the frozen section examination suggests that the cancer cells are very close to the margin of the surgical specimen, the surgeon is alerted that the "margins are not clear" and that additional tissue needs to be removed to insure that the entire cancer is gone from the body. Theoretically, the surgeon could have the patient ready on the operating room table for additional removal of tissue pending the pathologists' opinion as to whether this additional removal is needed. In practice, because frozen section examination is fairly inaccurate, most surgeons will not rely on the information from frozen section examination, and will simply complete their surgery and hope that when the final pathological report comes out (several days after surgery) the margins will have been shown to be clear of tumor. The risk of local recurrence of breast cancer is higher if the margins are not clear and if re-excision is not done. As a result, for breast cancer resections, in as many as 30% of cases, a re-excision is needed because the final pathology report comes back saying that the margins were not clear.
The present invention also pertains to the art of autoradiography. Autoradiography is a very old technique for using radiotracers in tissues to form images of radiotracer concentration in the tissues. Autoradiography is typically performed by injecting an animal with a radioactive tracer, sacrificing the animal, and then slicing the animal's organs up and imaging the sliced organs with a detector that is sensitive to radiation emitted by the radioactive tracer. In nearly all cases, the autoradiography detector is sensitive to beta rays emitted by a radioactive tracer. The notable feature of autoradiography is that the specimen is placed in contact with the radiation detector, thereby improving spatial resolution.
The present invention also pertains to the art of radiotracer imaging of human cancers. Radiotracers consists of a chemical compound containing a component that is biologically specific (i.e., binds to a specific type of receptor, cell or organ), and a second component that emits radiation which can be detected by a device placed external to the body. For breast cancer imaging, the most widely used radiotracers are the positron-emitter 2-[F-18]fluorodeoxyglucose (also known as FDG) and the single-photon emitter Tc-99m SestaMIBI (also known as MIBI). FDG can be detected with a positron emission tomography (also known as PET) scanner, or with a special device invented by the applying inventor known as a positron emission mammography scanner. MIBI can be detected with a gamma camera, or with a special device invented by the applying inventor known as a single photon emission mammography scanner. Several investigators have used hand-held gamma cameras or non-imaging gamma ray detectors in an operating room to examine the patient's body prior to removal of a cancer, and after removal of a cancer. No investigators have imaged the radioactive cancer after removal from the patient's body in order to assess whether the margins of resection were complete.
The present invention is novel in that it consists of the use of a radiation detector in conjunction with surgically-resected human tumors, in situations where the patient was injected with the cancer-seeking radiotracer prior to surgery. After the human tumor specimen is removed from the patient's body, it is either imaged whole (i.e., without slicing) or is sliced and then the slices imaged with the radiation detector. The radioactive tracer can either be a gamma emitter like Tc-99m labeled SestaMIBI, or it can be a beta emitter like 2-(F-18)Fluorodeoxyglucose.
The present invention is also novel in that it allows comparative imaging of the specimen by x-ray or other methods, and permits simultaneous display of the radiotracer and the x-ray images.
Nobody has imaged a human surgical specimen from a patient injected with radiotracers prior to surgery in order to describe the distribution of tumor in the specimen, and specifically to determine whether a tumor is wholly contained within the surgical specimen. Technically this approach is more easily accomplished than an intraoperative examination for several reasons: First, all the radiation is coming from the specimen when only the specimen is examined, whereas if we were to examine the tumor while it was in the patient we would have to remove the influence of radiation from parts of the body other than the surgical specimen. In the case of breast imaging, this "scatter" from parts of the body other than the breast is much greater than the radiation emitted by the breast, which can make it very challenging to see small tumors well.